Circular runways

[jwocky]

@Omega: Banking+centrifugal force should do the trick and make it actually easier. About the ILS problem, two thoughts: First of all, ILS stations are already now not always on the ends of the runways, ILS uses internally actually some shifting of the positions, it appears. But on the second thought, ILS will eventually anyway become obsolete the more GPS is used for virtually everything. With ILS you can bring a plane down actually plus/minus ten feet, with GPS+software in the flight computer, you can do basically about 0.1 feet. But more important, you can do non-linear approaches anyway. Means, on airports with a mountain in the way, you can actually guide the plane over the mountain and then in the descent. So, in longer terms, ILS as we know it today will be at least for the commercial planes become a thing of the past.

@HJ1AN: 15,000ft sounds wild, I know, but the point is, if you look at big airports and you measure from the most extreme points of all runways, those airports have actually almost now often a bigger diameter, only it's not round. As I posted some days ago, I don't think, this whole idea is feasible for smaller airports anyway, but those have usually not 747s and A380s coming in. Probably not even 777s.

What I try here is actually making up my mind. I see some pros and some cons. Omega is right to be worried about pilot training ... but then, as KL-666 pointed out a hundred times, we have already now, with straight runways a lot of reasons to be worried about that. Talking Air Asia and Airbus-philosophies here. We are currently in a stage of development, one wonders, shall we bet on badly trained pilots or badly programmed computers. In my experience, people develop ideas, like those circular runways, under an implicit assumption of optimal conditions and the firm belief, everything is built like it was planned and everybody does his job right under all conditions. Which in reality is rarely the case. So I am not so much worried about planes sliding sideways over some ice spot on the runway after they stopped already. I am also not so much worried here about a touch down of 150 tons of plane on such an ice spot. Since the plane comes in slightly banked anyway, it has enough turn momentum to get over it and to be pressed into the runway again by the bankment. No, what still worries me is the idea to have a big concrete thing with tunnels under it. See, some smart guy calculates, it is no problem. A plane of 150, even 200 tons at lets say 150 knots doesn't produce enough force to cave in the tunnel with the traffic way under the runway. Then, they build it and what happens? Actually, not one plane, but some hundred per week rumble over this spot of the runway. Each of them alone is not heavy enough or fast enough to cause significant damage. Some little cracks at best. Even the occasional emergency landing at 160 knots or the occasional overloaded plane and the superheavy taking off is not a problem in itself. But after say five years and ten-thousand plane movements later, all those little cracks add up and a plane disappears in a sinkhole. A very special sinkhole because at it's bottom is a four or six lane traffic way with some hundred cars. I think, the developers of this idea have thought about planes only, not the airport infrastructure as a whole. We all remember airports in some places in the early 80s when planes got bigger and the passenger numbers soared. They extended runways, installed bigger jetways, they even built more restaurants, but it took them ten years to actually organize the passenger streams in the terminals. The circular runway idea is similarly only focused on the planes. But you end up with having a concrete ring around an airport, a ring, the people getting to the airport can't cross. So there have to be tunnels and I would really like to see the static calculations and the dynamic load calculations for those.

[SHM]

I really don't think circular runways are going to be seen in the future.

P.S As long as you have proper understanding of the systems of the airbus in detail, they're really safe.

[KL-666]

As long as pilots still touchdown halfway the runway, this is not going to work. Watch the film and see how "short" the touchdown zone on the visible circle segment is on approach. A late touchdown would result in the pilot having to follow the circle. I do not have much confidence in such maneuver. Specifically not when there is some wind, resulting in changing x-wind while following the circle on late touchdown.

Edit:

If people are so scared of a bit x-wind, then have a star with many straight runways. e.g. With an eight pointed star you have double rw's in many directions. Here is your "circle", with a diameter not much bigger than a real circle.



Kind regards, Vincent

[jwocky]

With the advantage that you can use the inactive runways (the ones in the cross wind) as taxiways. True, Vincent.

And SHM, that is exactly the problem: Airbus market under the hand, the airlines can save on pilot training, not that they need a proper understanding.

[HJ1an]

@HJ1AN: 15,000ft sounds wild, I know, but the point is, if you look at big airports and you measure from the most extreme points of all runways, those airports have actually almost now often a bigger diameter, only it's not round. As I posted some days ago, I don't think, this whole idea is feasible for smaller airports anyway, but those have usually not 747s and A380s coming in. Probably not even 777s.

I think you meant to respond to IAHM-COL's post..

For smaller airports, such as regional airports with only one runway, it is going to be a big waste of space. Instead of a long thin rectangular land use, you have a huge radius... so that made no sense already there

Anyway, for larger airports, which actually used up land sizes similar to a circle, if budget allows it, they might as well do the octagonal shape thing that KL-666 metioned.. however, I personally don't like intersecting runways and taxiway, so in my view they should move the outermost runways outwards without intersecting the runways.

[Omega]

Centrifugal force is insignificant as the aircraft slows down to a slower speed, making the inclined surface extremely dangerous when icy.



I'm assuming what you are thinking of is an LDA approach, in which the localizer course varies by just a few degrees, but never on a 90 degree angle from the runway.

[jwocky]

@HJ1AM: Right, my bad!

@Omega: No actually, I don't think about an LDA approach. The thing with the centrifugal force is, the mass of an airplane so big, that the centrifugal force is always bigger than the force created by sliding against the side friction of the tires to the inside of the circle. And the more the plane slows down, the more weight comes actually of the tires because the plane loses lift and this, the side friction of the tires grows.
Having said that, the problem in this is the third force in the system, the force created by the engines. This is by far the biggest of all three and if a pilot manages, because he had a spot with some grip, to direct the nose of his plane too far inside or outside and tries to stabilize by applying throttle, off he goes. In so far, I see the problem of icy circular runways, which for all practical reasons would be higher than on straight runways. So, technically, to be sure, that whole giant structure would need to be heated in winter or made ice-free by other measures. Which is what most airports try anyway by the extensive use of salt.
The ILS problem is more complex than I initially thought though because ILS is in tis basics quite primitive. Basically LOC and GS do the same thing, each sends two lobes with different modulation on the same frequency, which means, it actually depends on the place where the senders are. The bigger problem however, since the plane basically measures the overlap of those two lobes, it can be only linear. So, the whole shebang would need to go on a mobile device along the runway to adapt to the use which is in itself an adaption to the current wind direction. Which would be theoretical possible ... but imagine, you have planes in the air already on localizer while you move that thing. It would be as if you pull the carpet under their feet. Whihc means, the idea would be only usable, if at all, when GPS based systems replace ILS, which will not happen the next ten or twetny years, I guess.